JPS6359469B2 - - Google Patents

Description

Detailed Description of the Invention This invention is a pulse compression radar that performs pulse compression reception without weighting during long-range reception, and performs weighted pulse compression reception during short-range reception to detect long-range targets. This relates to something that aims to improve performance.

Conventionally, there has been a pulse compression radar of this type as shown in FIG. In the figure, 1 is an antenna;
2 is a transmission/reception switch, 3 is a transmitter, 4 is a signal generator,
5 is a receiver, 6 is a pulse compression circuit, 7 is a detector,
8 is an indicator. As shown in FIG. 2, the pulse compression circuit 6 is composed of a weighting function filter 6a and a pulse compression delay line 6b, and the weighting function filter 6a weights the output of the receiver 5.
The pulse compression delay line 6b is connected to this weighting function filter 6.
This is to pulse-compress the output of a.

Next, the operation will be explained using FIG.

The signal generator 4 generates a high frequency pulse signal in an intermediate frequency band, and frequency modulation is applied within the pulse as shown in FIG. 3 a or b to obtain a signal shown in FIG. 3 c or d. This signal is converted into a microwave by the transmitter 3, power amplified, and sent to the antenna 1 via the transmitter/receiver switch 2.
radiated into space.

The signal reflected by the target in space is received by the antenna 1 and is applied to the receiver 5 via the transmitter/receiver switch 2.
First, the signal is high-frequency amplified in a high-frequency band, and then frequency-converted to an intermediate frequency inside the receiver 5. This conversion to an intermediate frequency is performed by using the same signal used for frequency conversion of the transmitted signal as a local oscillation signal inside the transmitter 3, and as a result, the influence of fluctuations in the local oscillation signal can be offset.

The signal converted to an intermediate frequency is amplified inside the receiver 5 and applied to the pulse compression circuit 6.

This pulse compression circuit 6 usually has a configuration as shown in FIG. 2, and the weighting function filter 6a is a filter designed to attenuate the signal from the center to the periphery of the frequency spectrum of the signal, such as Taylor distribution, etc. Attenuates the signal from the center to the periphery by applying weights such as binomial distribution. This kind of processing is called weighting, and its effect will be described later. Weight function filter 6a
The output of is applied to the pulse compression delay line 6b, where the pulse is compressed. This pulse compression delay line 6b
are shown in Fig. 4 a, for each signal shown in Fig. 3 c, d.
A frequency versus delay time characteristic as shown in FIG. 2B is used, and is selected so that the delay time becomes shorter as the frequency increases so as to inversely compensate for the time given to each frequency component during transmission. Therefore, by passing through such a delay line 6b, each frequency component of the pulse signal is spread from t ₁ to t ₂ at the time of transmission, as shown in FIG. As shown in c or d of the same figure, pulse compression is concentrated at one location. At this time, as can be seen from FIG. 5, the main lobe m should become the original pulse, and all the energy should be concentrated here, but the side lobe s also appears. In order to suppress this sidelobe s, the sidelobe is suppressed by the aforementioned weighting function filter 6a, but at the same time, the amplitude of the mainlobe is also reduced. The optimal weighting function is said to be the Taylor distribution, but when this distribution is used, the amplitude of the main lobe is lowered by 1.0 to 1.5 dB, and this loss directly leads to deterioration of detection performance.

Conventional pulse compression radars are configured as described above, so when applying weighting to suppress range side lobes, the main lobe is
This resulted in a loss of 1.5 dB, and the detection performance deteriorated because the main lobe was used to detect the target.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above. Focusing on the fact that the harmful effects of range side lobes occur only at short range, The present invention aims to provide a pulse compression radar that can prevent deterioration in detection performance by bypassing a weighting function filter so as not to apply weighting when detecting a long-distance target.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 6 shows a pulse compression radar according to one embodiment of the invention. In the figure, the same reference numerals as in FIG. 1 indicate the same parts as in FIG.
The main difference is that the structure has been changed to that shown in the figure. Reference numeral 6c is a switch that allows only signals from a short distance to pass through the weighting function filter 6a, and applies signals directly to the pulse compression delay line 6b for signals from a long distance. This switch 6c obtains a timing signal from the signal generator 4 that is generated at a time corresponding to a distance where range sidelobes do not become a problem, and switches whether the received signal is passed through the weighting function filter 6a or bypassed. It's on.

Note that the operation of other parts is the same as that of the conventional one.

Next, the operation will be explained.

As mentioned above, the generation of range side lobes in pulse compression waveforms is difficult to avoid in principle.
In particular, for strong reflected waves from targets at short distances, as shown in the pulse compression waveform in Figure 8, the side lobe s becomes a strong signal level in absolute level even if it is at a relatively low level compared to the main lobe m. Even if there is a single target on the device, as shown in FIG. 9, false images d are generated before and after the real image r generated by side lobes. Normally, when the weight function filter 6a is not used,
Side lobes occur at a level approximately 13 dB lower than the main lobe, and with this level difference, in actual operation, a fairly strong false image will occur at short distances. Therefore, the side lobe is suppressed to about 30 dB using the weighting function filter 6a, and the system can be operated without causing any practical problems.

However, by using such a weighting function filter 6a, the main lobe is attenuated by approximately 1.0 to 1.5 dB, and the detection performance is degraded accordingly. This effect is particularly noticeable for long-distance targets, resulting in a decrease in detection distance.

In order to eliminate these drawbacks, we focused on the fact that for long-distance targets, the absolute level of the signal is low, and the sidelobes are buried below the noise level, so there is no need to improve the sidelobe ratio that much. The weighting function filter 6a of the pulse compression circuit 6 is bypassed during target reception.
Such operations reduce the loss of the main lobe from 1.0 to
It can eliminate 1.5dB, and the detection distance is 6~
A 9% increase in detection distance can be achieved.

In addition, the switching operation of the weighting function filter 6a is performed by generating a transmission signal with the signal generator 4, and then generating a timing trigger at a time delayed from the transmission signal by a time corresponding to a distance where sidelobes are not a problem. The switch 6c is operated within each sweep time of 8, and the signal that does not pass through the weighting function filter 6a after the timing trigger is selected and displayed on the indicator 8 for each sweep.

As described above, according to the present invention, since side lobes are suppressed by weighting only for target reception at short distances, the detection range is not affected by side lobes and the detection distance is not degraded.
It has the effect of making it possible to detect targets and eliminating the drawbacks of conventional pulse compression radar.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional pulse compression radar, FIG. 2 is a block diagram showing the pulse compression circuit of FIG. 1, and FIG. 3 is a diagram showing the frequency modulation operation performed by the signal generator and the output waveform. FIG. 4 is a diagram showing pulse compression delay line characteristics, FIG. 5 is a diagram showing pulse compression operation, FIG. 6 is a block diagram showing a pulse compression radar according to an embodiment of the present invention, and FIG. 7 is a diagram showing pulse compression radar according to an embodiment of the present invention. 8 is a diagram showing the main lobe and side lobes of the output of the pulse compression circuit of FIG. 6, and FIG. 9 is a diagram showing a real image and a false image on the indicator. 5... Receiver, 6... Pulse compression circuit, 6a... Weight function filter, 6c... Switch, 6b... Pulse compression delay line. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. In a pulse compression radar that uses for transmission and reception a signal in which frequency modulation is applied linearly or stepwise within the time width of a high-frequency pulse signal, or a signal in which the internal arrangement of the stepwise frequency modulation signal is changed, A receiver that receives reflected waves, a weighting function filter that weights the output signal of this receiver, and the output of the receiver and the output of the weighting function filter are input, and when receiving a short-range target, the signal is input from the weighting function filter. and a pulse compression circuit consisting of a pulse compression delay line that pulse-compresses the output of this switch. Pulse compression radar.